1. Field of the Invention
The present invention relates to a camera system, a master camera device, and a slave camera device.
2. Description of the Related Art
Conditions for watching live video from a surveillance camera device through a network are different from those for watching video on a video hosting website. For example, when watching video on a video hosting website, a delivered video stream is temporarily stored in a memory without being reproduced soon. In a case where a certain amount of video data is stored in the memory, the video data stored in the memory is read and reproduction thereof is started. Therefore, watching video on a video hosting website is not influenced by network traffic congestion, and stable reproduction is enabled.
In contrast, for example, when watching live video from a surveillance camera system in a parking area, a shopping mall, or the like, a captured image needs to be displayed instantly (needs to be displayed in real-time), and storage of the captured image in a memory is not allowed as in the case of the video on the video hosting website. Thus, in the surveillance camera system, network traffic congestion causes loss of smoothness in video due to discontinuous image, and packets of the captured image are disadvantageously discarded at last.
WO 2012/011301 A discloses a technology of grasping network congestion and controlling network traffic. According to WO2012/011301 A, traffic between a transmission end and a reception end is controlled based on packet discard information from a network switch.
However, discarding packets is a worst case finally generated by the network traffic congestion. Therefore, the technology according to WO 2012/011301 A represents a technology of controlling traffic after the worst case of discarding packets. Accordingly, in the technology according to WO 2012/011301 A, it is difficult to improve, for example, loss of smoothness of video caused by an unstable frame transmission interval occurring in initial congestion of the network traffic.
Further, in the technology according to WO 2012/011301 A, cameras are controlled through a repeater such as a switch. Therefore, even if an attempt is made to simultaneously control the cameras using multicast communication, the repeater such as a switch may block a control signal through the multicast communication. Accordingly, in the technology according to WO 2012/011301 A, control needs to be performed by designating the cameras one by one, and the control is inefficiently performed.
Therefore, the present invention provides a camera system, a master camera device, and a slave camera device which provide efficient communication, improving a transmission condition at an initial stage of an unstable transmission condition, providing a preferable real-time image.